Texas authorities charged a US Border Patrol supervisor with murder following what they called a two-week serial killing spree that left four female sex workers dead and ended when a fifth woman escaped at a service station and found help.

Juan David Ortiz, 35, an intelligence supervisor for the US Border Patrol, was charged with four counts of murder as well as aggravated assault and unlawful restraint, Webb County District Attorney Isidro Alaniz said in a tweet.

DA’s Office reports Juan David Ortiz, BP agent has been arrested for a series of murders & charged with aggravated assault, unlawful restraint & 4 cts of murder. We will continue working diligently w/ WCSO, DPS & Texas Rangers during this investigation.

State troopers found Ortiz hiding in a truck in a hotel car park in Laredo at around 2am Saturday. The border city about 235km (145 miles) southwest of San Antonio.

“We do consider this to be a serial killer,” Alaniz said.

Alaniz said that after the suspect picked up the fifth woman she quickly realised that she was in danger.

“When she tried to escape from him at a service station that’s when she ran into a (state) trooper,” Alaniz said.

He said that authorities believe Ortiz had killed all four women since September 3. The names of the victims were not immediately released.

Alaniz said two of them were US citizens but the nationalities of the other two were not yet known. All of them were working as prostitutes and one was a transgender woman, he said.

“The manner in which they were killed is similar in all the cases from the evidence,” said Alaniz.

He declined to discuss the evidence or say how the women were killed.

The bodies of two of the women were discovered this month along Interstate 35 in rural northwest Webb County, the Laredo Morning Times reported, while the third and fourth were found in the same area this weekend.

Alaniz said investigators are still trying to determine a motive for the killings. Authorities said they believe Ortiz acted alone.

“It’s interesting that he would be observing and watching as law enforcement was looking for the killer, that he would be reporting to work every day like normal,” Alaniz said.

Ortiz was a 10-year veteran of the Border Patrol.

US Customs and Border Protection issued a statement saying that it was fully cooperating with the investigation.

“Our sincerest condolences go out to the victims’ family and friends. While it is CBP policy to not comment on the details of an ongoing investigation, criminal action by our employees is not, and will not be tolerated,” the agency said.

The Texas Department of Public Safety, whose Texas Rangers are investigating, did not return several messages seeking comment.